This invention relates to electronics in general and more particularly to liquid crystal displays.
The need for artificial horizons and other attitude indicating instruments in aviation has long been recognized. Under conditions of reduced visibility such as fog or during nighttime flying, the Federal Aviation Administration requires that the flight must be conducted in accordance with instrument flight rules (IFR). Even under visual flight rules (VFR), many pilots find an attitude indicator helpful. An attitude indicator shows the relative pitch of the nose of the aircraft, up or down relative to the axis of motion of the aircraft, and roll of the aircraft around its axis of motion so that the pilot may readily coordinate turns and determine the relative attitude of the aircraft relative to the surface of the earth and the axis of motion.
Another helpful instrument is a flight director which provides commands informing the pilot how to position the aircraft attitude in order to achieve some prescribed flight activity, for example capturing an instrument landing system (ILS) beam. The combination of these two instruments is termed attitude director indicator, or "ADI".
Another helpful instrument in virtually all modern aircraft is the heading indicator, formerly constructed with a magnetic compass but more recently being supplemented by gyrocompasses. Other variables such as speed of the aircraft, VHF omnirange information or "VOR", and instrument landing system or "ILS" information such as localizer deviation, glideslope and approach speed to an ILS runway may also be shown.
Typically, a combined attitude director (ADI) showing attitude and ILS information was used in conjunction with a course indicator showing heading and VOR information to provide a relatively complete instrumentation system for an aircraft. These devices, however, utilized a relatively large number of mechanical devices such as synchros, relays, and complex gearing structures to provide a mechanical indicator for the pilot having as many as ten or more moving indicators displayed on an indicator as small as 4.times.4 inches. These displays necessitated extreme measures in mechanical engineering to place the gearing structures and motors required within the space requirement for avionics displays as well as exacted a relatively severe weight penalty in the aircraft.
The advent of the cathode ray tube in avionics displays provided for simplified mechanical structure and enabled a significant increase in flexibility for the avionics display designer in allowing both numeric data and analog displays to be presented on the cathode ray tube. The CRT, however, requires a relatively deep assembly to attain precision deflection and requires a relatively heavy power supply to provide the voltages necessary to drive the CRT.
The use of liquid crystal displays in avionics is known for presenting numeric data such as frequencies or heading information as well as an analog display such as a bar graph indicating fuel levels. The liquid crystal display technology, however, is limited to producing images that cannot be physically moved over the display, in contrast to CRT technology or the mechanical motion displays, since the segments of the liquid crystal are permanently deposited on the surface of the g1ass. Therefore, the industry has heretofore been unable to adopt the advantages of liquid crystal displays such as relative low cost, ease of manufacture, long mean-times-before failure, and high readability into an avionics display unit capable of displaying relative motions.